1. Field of the Invention
The present invention relates generally to a switch mechanism for key-entry operation and, more particularly, to a key-entry switch (hereinafter referred to as a key switch) preferably used for a keyboard incorporated as an input device in electronic equipment. The present invention also relates to a relatively thin keyboard provided with a plurality of key switches.
2. Description of the Related Art
In the technical field of portable electronic equipment such as notebook-size personal computers or word processors, etc., various techniques have been provided to facilitate a reduction in height or thickness of an equipment housing including a keyboard and to improve the portability of the equipment. Particularly, when the height of a keyboard provided with a plurality of key switches is to be reduced, it has been generally required to maintain the stroke of each key switch at a predetermined distance to ensure constant operational properties thereof and, simultaneously, to reduce the entire height of the key switch upon both the non-operated (or switched-off) and operated (or pushed down and switched-on) condition thereof.
There has been known a conventional key switch, for use in such a relatively thin keyboard, which includes a base, a key top disposed above the base, a pair of link members for supporting the key top above the base and directing it in the vertical or up-and-down direction, and a switching mechanism for opening and closing contacts of an electric circuit in correspondence to the vertical or up-and-down movement of the key top. The pair of link members are interlocked to each other, each being operatively engaged with both the base and the key top so as to allow the key top to be moved in a parallel displacement in a substantially vertical direction in relation to the major surface of the base, while keeping a predetermined posture of the key top. The switching mechanism comprises a sheet-like switch disposed beneath the base, and an elastic actuating member which is disposed between the key top and the sheet-like switch and which operates so as to close the contacts in the sheet-like switch as the key top is moved downward.
As the elastic actuating member, in general, a dome-like member integrally formed from a rubber material is widely employed. When no external force is applied to the key top, the dome-like elastic actuating member supports the key top on the outer surface of the dome upper end, and urges the key top toward an initial position vertically upwardly away from the base. When the key top is pushed downward by a key-entry operation, the elastic actuating member is elastically deformed while exerting a biasing or an elastic restoring force to the key top in an opposite direction. In this condition, a protrusion formed on the interior surface of the dome upper end serves to push a pair of contacts in the sheet-like switch from its outer surface, so as to close or turn-on the sheet-like switch. When the downward pushing force applied to the key top is released, the elastic actuating member is elastically restored, so as to return the key top to the initial position and to open or turn-off the contacts in the sheet-like switch.
The dome-like elastic actuating member can exert, when it is elastically deformed by a key-entry operation, a biasing or an elastic restoring force to the key top, which assumes non-linear relationship with a displacement of the key top due to its dome-shaped profile. That is, the key switch can establish such a key-entry operating properties that at the instant when the pushed-down displacement of the key top exceeds a predetermined value, the biasing force, which has been gradually increased until that time, is sharply reduced. As a result, an operator can easily recognize that the key switch has been correctly and appropriately operated, by finger pressure, even when the keyboard is one adapted to be incorporated in a portable electronic equipment in which the key switch generally has a relatively short keying stroke. The dome-shaped elastic actuating member is, however, held in a location between the key top and the sheet-like switch and interposed therebetween in relation to the height of the key switch, regardless of the degree of the deformation of the actuating member. Therefore, the dome-shaped elastic actuating member in itself affects the entire height of the key switch upon both the inoperated and operated condition thereof, and thus tends to become a major factor that hinders further reduction in the height or thickness of the key switch, and hence of the keyboard. An alternative construction of the dome-shaped elastic actuating member has, therefore, been proposed which does not affect the entire height of the key switch in both the inoperated and operated condition thereof.
For example, Japanese Unexamined Patent Publication (Kokai) No. 10-334760 (JP-A-10-334760) discloses one example of a key switch in which at least one of a pair of frame-like link members and a base supporting these link members is formed from an elastic material such as a thin elastic metal sheet. The pair of link members are elastically supported between the base and the key top by a cantilever spring formed on the lower end portion of at least one of the frame-like link members, or on at least one of the supporting portion of the base supporting the lower end portion of the frame. When the key top is pushed down by a key-entry operation, a horizontal displacement of the lower end portion of the frame-like link member causes the deflection of the cantilever spring, and produces an elastic restoring force, which is transmitted via the link members to the key top and exerts a biasing force, onto the key top, upwardly and toward the initial position. In this construction, another cantilever spring is formed at one of the link members for pushing the pair of contacts in the sheet-like switch, thus eliminating the dome-shaped elastic actuating member.
The cantilever spring which is used as the key top biasing means, as described above, is thought to contribute to the reduction of the entire height of key switch in both the inoperated and operated condition thereof, since, unlike the dome-shaped elastic actuating member, it is not interposed between the key top and the sheet-like switch in relation to the height of the key switch. This cantilever spring, however, produces the elastic restoring force mainly in generally flat spring portion between the proximal end connected to the link member or the base and the free distal end thereof. As the key top moves downward, the generally flat spring portion of the cantilever spring is deflected in substantially the same direction as the shifting mortion of the lower end portion of the frame-like link member. Thus, the length of the spring portion of the cantilever spring is relatively short corresponding to the width (in the direction perpendicular to the shifting direction) of the lower end portion of the frame-like link member.
With this construction, in order to reduce the dimension of the key switch, it is required to reduce the dimension of the cantilever spring, and hence to shorten the length of the spring portion thereof. As a result, among key switches having different dimensions, the elastic restoring force of a key switch having a smaller dimension tends to be unnecessarily increased for the same amount of deformation, that is, for substantially same length of depressed key stroke, compared to a key switch having a greater dimension. Thus, there arises a problem that the size reduction of a key switch entails an unnecessary increase in the elastic biasing force exerted onto the key top toward the initial position, and adversely affects the key-entry operating properties. In addition, the degradation of the durability of the cantilever spring, due to the increased bending stress, is also of concern.
In order to achieve the desired key entry operating properties, it is required, of the cantilever spring as the key top biasing means, that it exerts, in cooperation with the link members, a biasing force which assumes the same non-linear relationship with a displacement of the key top as the dome-shaped elastic actuating member. In order to satisfy this requirement, it is advantageous that the cantilever spring has some degree of freedom in design, that is, the optimal dimension and geometry of the cantilever spring for exerting a desired biasing force can be selected from a range of values. With the above construction, however, a size reduction of the key switch entails a size reduction of the cantilever spring so that the design freedom is also decreased and it may become difficult to exert a desired biasing force, onto the key top, in a non-linear relationship with the displacement of the key top.
There has been known a key switch having the above described construction in which each of the pair of link members have, at one end region thereof, an engaging shaft portion rotatably or slidably engaged with the base, and at the other end region thereof, an engaging shaft rotatably or slidably engaged with the key top. In this construction, the base and the key top have both bearing portions formed thereon for receiving individually the respective engaging shaft of the link members. In this case, the engaging shafts are required to rotate or slide smoothly in respective bearing portions. In the case where an unnecessary gap is formed between the bearing portion of the key top and the engaging shaft of the link member due to the dimensional errors in the shaping of the key top and the link member, there arises a fluctuation of the key top during key-entry operation. Especially when the key top is in the initial position, that is, in the uppermost position in the key-entry stroke, the fluctuation of the key top with respect to the link member may cause the key top to be inclined from the normal position when the key top is pushed down by an operator, and cause the contacts in the sheet-like switch to be pushed down incorrectly. If the machining precision is to be increased, with a smaller tolerance for the key top and the link member, to avoid this problem, the production cost of the key switch may be increased.
It is therefore an object of the present invention to provide a key switch, using a pair of link members as supporting/directing means for the key top, in which a simple and inexpensive construction permits further reduction of the entire height of the key switch in both the inoperated and operated conditions, and eliminates the dome-shaped elastic actuating member without impairing the non-linear key-entry operating properties of the key switch, and which can avoid an unnecessary increase of the biasing force elastically biasing the key top toward the initial position when the dimension of the key switch is reduced.
It is another object of the present invention to provide a key switch, using a pair of link members as supporting/directing means for the key top, in which the fluctuation of the key top with respect to the link members is reduced as much as possible without requiring high dimensional precision for the key top and the link members.
It is a further object of the present invention to provide a keyboard, provided with a plurality of key switches as described above, in which a further reduction in the height or thickness, as well as an improvement in portability and improvement in key-entry operability, are achieved.
In accordance with the present invention, there is provided a key switch comprising a base; a key top arranged above the base; a pair of link members interlocked to each other and operatively engaged with the base and the key top to support the key top above the base and direct the key top in a vertical direction, each of the link members including a sliding portion slidably and shiftably engaged with either one of the base and the key top; at least one plate spring disposed between at least one of the link members and either one of the base and the key top with which the sliding portion is engaged, to exert a biasing force, relative to a shifting amount of the sliding portion, onto the at least one of the link members in a direction different from the vertical direction, each of the at least one plate spring including, in an integral manner, a first spring portion extending along a fixed-end side in a direction substantially parallel to a shifting direction of the sliding portion of each link member and a second spring portion extending along a free-end side in a direction intersecting the first spring portion; and a switching mechanism for selectively opening and closing an electric circuit in connection with a vertical movement of the key top.
At least one plate spring may be fixed, at a proximal end of the first spring portion, to the at least one of the link members and abutted at a part of the second spring portion onto the base.
Alternatively, at least one plate spring may be fixed, at a proximal end of the first spring portion, to the base and abutted at a part of the second spring portion onto the at least one of the link members.
The base may include a fixed base element engaged with the pair of link members and a movable base element disposed under the fixed base element in such a manner as to be movable with relation to the fixed base element.
In this arrangement, at least one plate spring may be fixed at a proximal end of the first spring portion to the at least one of the link members and abutted at a part of the second spring portion onto the movable base element.
Alternatively, at least one plate spring may be fixed at a proximal end of the first spring portion to the movable base element and abutted at a part of the second spring portion onto the at least one of the link members.
In one aspect of the invention, the pair of link members are arranged to mutually intersect and are pivotably connected relative to each other at an intersection thereof. In this aspect, a first one of the link members is slidably engaged at one end region thereof with the base and rotatably engaged at another end region thereof with the key top, the sliding portion being provided on the one end region of the first link member, and a second one of the link members is engaged rotatably at one end region thereof with the base and slidably at another end region thereof with the key top, the sliding portion being provided on the other end region of the second link member.
In another aspect of the invention, the pair of link members are arranged to mutually intersect and are pivotably and slidably connected relative to each other at an intersection thereof. In this aspect, each of the link members is slidably engaged at one end region thereof with the base and rotatably engaged at another end region thereof with the key top, the sliding portion being provided on the one end region of each link member.
In further aspect of the invention, the pair of link members are meshed with each other at a toothed end of each of the link members. In this aspect, each of the link members is slidably engaged at one end region thereof with the base and rotatably engaged at another end region thereof with the key top, the sliding portion being provided on the one end region of each link member, the toothed end being provided adjacent to the other end region of each link member.
The present invention also provides a key switch comprising a base; a key top arranged above the base; a pair of link members interlocked to each other and operatively engaged with the base and the key top to support the key top above the base and direct the key top in a vertical direction, each of the link members including an axle engaged with the key top and an extension provided adjacent to the axle; and a switching mechanism for selectively opening and closing an electric circuit in connection with a vertical movement of the key top; wherein the link members are arranged in such a manner that, when the key top is in an upper limit position of a key-entry stroke, extensions provided in the link members are substantially in contact with the key top at respective areas extending further than the distance between axles of the link members.
It is preferred that the extension comprises an elastic member.
In one aspect of the invention, the pair of link members are arranged to mutually intersect and are meshed with each other at an intersection thereof. In this aspect, each of the link members is engaged slidably at one end region thereof with the base and rotatably at another end region thereof with the key top, a second axle being provided on the one end region of each link member, the first-mentioned axle and the extension being provided on the other end region of each link member.
The present invention further provides a keyboard comprising a plurality of key switches, each of the key switches being one as defined above.